Valve holder and loading integration

ABSTRACT

A device for holding an implantable medical device includes a jar for receiving the implantable medical device, and a ring coupleable to the jar. The ring has a plurality of channels adapted to receive retaining features of the implantable medical device to stabilize the medical device within the jar.

CROSS REFERENCE TO RELATED APPLICATION

The application claims the benefit of the filing date of U.S.Provisional Patent Application No. 61/713,213 filed Oct. 12, 2012, thedisclosure of which is hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to heart valve replacement and, inparticular, to heart valve loading and storage. More particularly, thepresent invention relates to devices and methods for holding,transferring and deploying prosthetic heart valves.

Prosthetic heart valves that are collapsible to a relatively smallcircumferential size can be delivered into a patient less invasivelythan valves that are not collapsible. For example, a collapsible valvemay be delivered into a patient via a tube-like delivery apparatus suchas a catheter, a trocar, a laparoscopic instrument, or the like. Thiscollapsibility can avoid the need for a more invasive procedure such asfull open-chest, open-heart surgery.

Collapsible prosthetic heart valves typically take the form of a valvestructure mounted on a stent. There are two types of stents on which thevalve structures are ordinarily mounted: a self-expanding stent and aballoon-expandable stent. To place such valves into a delivery apparatusand ultimately into a patient, the valve must first be collapsed orcrimped to reduce its circumferential size.

Despite the various improvements that have been made to the collapsibleprosthetic heart valve delivery process, conventional storage, transferand delivery techniques suffer from some shortcomings. Ideally,prosthetic heart valves are properly packaged at the manufacturingfacility to ensure that the arriving valve performs as intended, andthat the design and the quality of the valve is not compromised duringdelivery. However, in conventional prosthetic heart systems, the valvemay sometimes be damaged during delivery. In addition to physical damageof the prosthetic heart valve during shipping and handling, valves mayalso be contaminated as they are transferred from storage or duringimplantation in the patient.

There therefore is a need for further improvements to the devices,systems, and methods for transcatheter storage and delivery ofcollapsible prosthetic heart valves. Among other advantages, the presentinvention may address one or more of these needs.

SUMMARY OF THE INVENTION

A device for holding an implantable medical device may include a jar forreceiving the implantable medical device and a ring coupleable to thejar, the ring having a plurality of channels adapted to receiveretaining features of the implantable medical device to stabilize themedical device within the jar.

In some examples, the ring further comprises a plurality of openingsthrough which a liquid may be drained from the jar. The jar may includea plurality of clips and the ring includes a plurality of indentationscapable of mating with the clips to lock the ring to the jar. Theplurality of clips may be evenly spaced about a circumference of the jarand the plurality of channels may extend radially in the ring. In somevariations, the channels may extend circumferentially or may be angled.The plurality of channels may include three channels and may be adaptedto receive a circular retaining feature of the implantable medicaldevice.

The plurality of channels may be adapted to receive a diamond-shapedretaining feature of the implantable medical device. The plurality ofchannels may be adapted to receive a square-shaped retaining feature ofthe implantable medical device.

In some embodiments, a device for transporting an implantable medicaldevice may include a ring coupleable to the implantable medical device,the ring having a plurality of channels adapted to receive retainingfeatures of the implantable medical device. The ring may further includea plurality of openings through which a liquid may be drained from thejar. The plurality of channels may extend radially in the ring. Theplurality of channels may include three channels.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the presently disclosed delivery system aredescribed herein with reference to the drawings, wherein:

FIG. 1 is a side elevational view of a collapsible prosthetic heartvalve showing the valve assembly attached to the stent;

FIG. 2 is an enlarged side elevational view of a retaining element of acollapsible prosthetic heart valve;

FIGS. 3A-E are enlarged side elevational views of alternate embodimentsof retaining elements;

FIG. 4 is a diagrammatic view of a stent disposed within a jar forstorage and/or transport;

FIG. 5 is a top view of a ring coupled to a jar containing the stent;

FIGS. 6A-6D is a series of retainer element-channel interfaces couplingthe stent to a ring;

FIG. 7A is a partial perspective view of a tool for decoupling the ringfrom the jar;

FIG. 7B is a partial perspective view of a tool and a threaded shaft fordecoupling the ring from the jar;

FIG. 7C is a partial perspective view of a press-fit shaft fordecoupling the ring from the jar;

FIG. 7D is a perspective view showing a ring being decoupled from thejar;

FIG. 7E is a perspective view showing the heart valve being rinsed;

FIG. 7F is a perspective view showing the heart valve being insertedinto the support member of a valve loading device; and

FIG. 7G is a partial perspective view showing a heart valve inserted inthe support member with the ring removed.

Various embodiments of the present invention will now be described withreference to the appended drawings. It is to be appreciated that thesedrawings depict only some embodiments of the invention and are thereforenot to be considered limiting of its scope.

DETAILED DESCRIPTION

As used herein, the term “proximal,” when used in connection with aprosthetic heart valve, refers to the end of the heart valve closest tothe heart when the heart valve is implanted in a patient, whereas theterm “distal,” when used in connection with a prosthetic heart valve,refers to the end of the heart valve farthest from the heart when theheart valve is implanted in a patient.

FIG. 1 shows a collapsible prosthetic heart valve 100 according to anembodiment of the present disclosure. The prosthetic heart valve 100 isdesigned to replace the function of a native aortic valve of a patient.Examples of collapsible prosthetic heart valves are described inInternational Patent Application Publication No. WO/2009/042196; U.S.Pat. No. 7,018,406; and U.S. Pat. No. 7,329,278, the disclosures of allof which are hereby incorporated herein by reference. As discussed indetail below, the prosthetic heart valve has an expanded condition and acollapsed condition. Although the invention is described herein asapplied to a prosthetic heart valve for replacing a native aortic valve,the invention is not so limited, and may be applied to prosthetic valvesfor replacing other types of cardiac valves.

The prosthetic heart valve 100 includes a stent or frame 102, which maybe wholly or partly formed of any biocompatible material, such asmetals, synthetic polymers, or biopolymers capable of functioning as astent. Suitable biopolymers include, but are not limited to, elastin,and mixtures or composites thereof. Suitable metals include, but are notlimited to, cobalt, titanium, nickel, chromium, stainless steel, andalloys thereof, including nitinol. Suitable synthetic polymers for useas a stent include, but are not limited to, thermoplastics, such aspolyolefins, polyesters, polyamides, polysulfones, acrylics,polyacrylonitriles, polyetheretherketone (PEEK), ultra-high molecularweight polyethylene and polyaramides. The stent 102 may have an annulussection 110 adjacent a proximal end 150, an aortic section 130 adjacenta distal end 152, and a transition section 120 between the aorticsection 130 and the annulus section 110. Each of the annulus section110, the transition section 120 and the aortic section 130 of the stent102 includes a plurality of struts 114. Certain struts 114 may be joinedto form a plurality of cells 112 connected to one another around thestent. The annulus section 110 and the aortic section of the stent 102may include one or more annular rows of cells 112 connected to oneanother. For instance, the annulus section 110 may have two annular rowsof cells 112. The cells in the aortic section 130 may be larger than thecells in the annulus section 110. The larger cells in the aortic section130 better enable the prosthetic valve 100 to be positioned without thestent structure interfering with blood flow to the coronary arteries.When the prosthetic heart valve 100 is in the expanded condition, eachcell 112 may be substantially diamond shaped.

The annulus section 110 of stent 102 has a relatively smallcross-section in the expanded condition, while the aortic section 130has a relatively large cross-section in the expanded condition.Preferably, annulus section 110 is in the form of a cylinder having asubstantially constant diameter along its length. The transition section120 may taper outwardly from the annulus section 110 to the aorticsection 130.

The stent 102 may also include a plurality of commissure features 116for attaching the commissure between two adjacent leaflets to the stent.As can be seen in FIG. 1, the commissure features 116 may lie at theintersection of four cells 112, two of the cells being adjacent oneanother in the same annular row, and the other two cells being indifferent annular rows and lying in end-to-end relationship. Preferably,commissure features 116 are positioned entirely within annulus section110 or at the juncture of annulus section 110 and transition section120. Commissure features 116 may include one or more eyelets whichfacilitate the suturing of the leaflet commissure to the stent.

The prosthetic heart valve 100 also includes a valve assembly 104attached inside the annulus section 110 of the stent 102. United StatesPatent Application Publication No. 2008/0228264, filed Mar. 12, 2007,and United States Patent Application Publication No. 2008/0147179, filedDec. 19, 2007, the entire disclosures of both of which are herebyincorporated herein by reference, describe suitable valve assemblies.The valve assembly 104 may be wholly or partly formed of any suitablebiological material or polymer. Examples of biological materialssuitable for the valve assembly 104 include, but are not limited to,porcine or bovine pericardial tissue. Examples of polymers suitable forthe valve assembly 104 include, but are not limited to, polyurethane,ultra-high molecular weight polyethylene and polyester.

The valve assembly 104 may be secured to stent 102 by any suitableattachment means, such as suturing, stapling, adhesives or the like. Thevalve assembly 104 includes a cuff 106 and a plurality of leaflets 108which collectively function as a one-way valve. FIG. 1 illustrates aprosthetic heart valve for replacing a native tricuspid valve, such asthe aortic valve. Accordingly, prosthetic heart valve 100 is shown inFIG. 1 with three leaflets 108, as well as three commissure features116. However, it will be appreciated that the prosthetic heart valvesaccording to this aspect of the invention may have a greater of lessernumber of leaflets and commissure features.

Cuff 106 may be disposed on the lumenal surface of annulus section 110,on the ablumenal surface of annulus section 110, or on both surfaces,and the cuff may cover all or part of either or both of the lumenal andablumenal surfaces of the annulus section. FIG. 1 shows cuff 106disposed on the lumenal surface of annulus section 110 so as to coverpart of the annulus section while leaving another part thereofuncovered. The cuff 106 may be wholly or partly formed of any suitablebiological material or polymer, such as ultra-high molecular weightpolyethylene or PTFE.

A first edge (not shown) of each leaflet 108 may be attached to thestent 102 by any of the various manners described above. For example,the first edge of each leaflet 108 may be sutured to the stent 102 bypassing strings or sutures through the cuff 106 of the valve assembly104. The cuff and/or sutures may be formed fromultra-high-molecular-weight polyethylene. A second or free edge 124 ofeach leaflet 108 may coapt with the corresponding free edges of theother leaflets, thereby enabling the leaflets to function collectivelyas a one-way valve.

As is shown in FIG. 1, the entirety of valve assembly 104, including theleaflet commissures, may be positioned in the annulus section 110 ofstent 102. When opened, the leaflets may extend further into thetransition section or may be designed such that they remainsubstantially completely within the annulus section. That is,substantially the entirety of valve assembly 104 may be positionedbetween the proximal end 150 of stent 102 and the commissure features116, with none of the valve assembly 104 positioned between commissurefeatures 116 and the distal end 152 of the stent.

It will also be noted that while the inventions herein described arepredominately discussed in terms of a tricuspid valve and a stent havinga shape as illustrated in FIG. 1, the valve could be a bicuspid valve,such as the mitral valve, and the stent could have different shapes,such as a flared or conical annulus section, a less-bulbous aorticsection, and the like, and a differently shaped transition section.

Stent 102 may include one or more retaining elements 118 at the distalend 152 thereof, the retaining elements being sized and shaped tocooperate with female retaining recesses provided on a deployment orstorage device. Additionally, the retaining elements 118 may be disposedat the proximal end 150 of the device or on both ends of the device. Theengagement of retaining elements 118 with the female retaining recesseson the deployment device helps maintain prosthetic heart valve 100 inassembled relationship with the deployment or storage device, minimizeslongitudinal movement of the prosthetic heart valve relative to thedeployment device during unsheathing or resheathing procedures, andhelps prevent rotation of the prosthetic heart valve relative to thedeployment device as the deployment device is advanced to the targetlocation and during deployment.

In operation, the embodiments of the prosthetic heart valve describedabove may be used to replace a native heart valve, such as the aorticvalve, a surgical heart valve or a heart valve that has undergone asurgical procedure. The prosthetic heart valve may be delivered to thedesired site (e.g., near a native aortic annulus) using any suitabledelivery device. During delivery, the prosthetic heart valve is disposedinside the delivery device in the collapsed condition. The deliverydevice may be introduced into a patient using a transfemoral,transapical, transseptal, transaxillary or any other percutaneousapproach. Once the delivery device has reached the target site, the usermay deploy the prosthetic heart valve. Upon deployment, the prostheticheart valve expands into secure engagement within the native aorticannulus. When the prosthetic heart valve is properly positioned insidethe heart, it works as a one-way valve, allowing blood to flow in onedirection and preventing blood from flowing in the opposite direction.

In a prosthetic heart valve, the valve assembly may be spaced from thedistal or aortic end of the stent by a distance that enables deploymentof the heart valve by an amount sufficient for the valve leaflets of theprosthetic valve to operate as intended, while the distal end 152 of thestent remains captured by the delivery device. More particularly, aswill be explained further below, the annulus end of the prosthetic heartvalve may be deployed first while the aortic end of the prosthetic heartvalve remains at least partially covered by the distal sheath of thedelivery device. The annulus portion of the prosthetic heart valve maybe deployed so that the entirety of the valve leaflets, up to andincluding the commissures, is deployed and fully operational. Bydeploying the prosthetic heart valve in this manner, the user candetermine whether the valve leaflets are properly positioned relative tothe native valve annulus, and whether the valve is functioning properly.If the user determines that the position and operation of the valve areacceptable, the remainder of the valve may be deployed. However, if itis determined that the leaflet position is improper or that the valve isnot functioning properly, the user may resheath the valve and eitherreposition it for redeployment, or remove it entirely from the patient.This can be particularly important in very high risk patients who wouldtypically be recipients of these types of valves, because of the natureof their condition and the impact that may have on the shape and/orcondition of the native valve and valve annulus.

FIG. 2 is an enlarged view of the retaining element 118 described inFIG. 1, above. As shown in FIG. 2, one or more struts 114 may terminatein a circular retaining element 118. Retaining element 118 may includean eyelet 210 used to position, transfer or adjust the position of thestent via a snare as will be described later. Retaining elements 118 mayalso be useful in implanting the heart valve 100 in a patient by matingto a delivery device as described above with reference to FIG. 1.

FIGS. 3A-E illustrate several variations of the retaining element shownin FIG. 2 to aid in storage, shipment, transfer and delivery of aprosthetic heart valve. FIG. 3A illustrates a first example of aretaining element 118 at the end of a strut 114, the retaining element118 being in the shape of a square. As with the retaining element shownin FIG. 2, square retaining element 118 may include one or more eyelets210. It will be understood that eyelet 210 need not be circular and thatvarious configurations of the eyelet, such as oval, triangular andsquare eyelets are contemplated. FIG. 3B illustrates a diamond-shapedretaining element 118 attached to a strut 114, the retaining elementhaving an eyelet 210. FIG. 3C illustrates an oblong retaining element118 having an elongated eyelet 210.

FIG. 3D illustrates a substantially semi-circular retaining element 118having a circular eyelet 210. Retaining element 118 may further includea pair of tabs 330 that form recesses 340 between tabs 330 and strut114. Recesses 340 may be used as additional members for snaring thestent during repositioning, loading and/or delivery. FIG. 3E illustratesyet another example of retaining element 118. The retaining element 118of FIG. 3E is circular in form but also includes a pair of separate tabs330 similar to those described in FIG. 3D. In contrast to the exampleshown in FIG. 3D, tabs 330 are formed as part of strut 114 and not aspart of retaining element 118. As previously discussed, retainingelement 118 may mate with female recesses on a deployment or deliverydevice. Thus, by forming tabs 330 on strut 114 instead of on retainingelement 118, the same deployment or storage devices may be used tocouple to the stents regardless of whether they include tabs 330.

FIG. 4 illustrates one method of storing and transporting a stent withina jar. As seen in FIG. 4, jar 450 may be sized slightly larger thanstent 400 and stent 400 may be placed in an upright position within thejar. A ring 500 may be placed on top of jar 450 to keep the stent 400from moving during delivery and/or storage. An additional top cap (notshown) may be disposed on top of ring 500 to seal and secure stent 400within jar 450.

Jar 450 may include a plurality of clips 460 which mate with a pluralityof indentations 510 on ring 500 to align the ring with jar 450. Clips460 may also help secure ring 500 to jar 450. Clips 460 may be pliableprongs that are simply bent over selected indentations of the ring.Alternatively, clips 460 may include spring clips which deform from aninitial position to facilitate mating with the indentations, and thenspring back into their original position within the indentations to holdthe ring 500 in place. Additional sutures may also be used to secure thestent. The jar may be filled with a preserving solution that immersesstent 400, such as glutaraldehyde, formaldehyde or an inert gas such asnitrogen.

FIG. 5 illustrates a top view of ring 500 coupled to jar 450. In theillustrated example, ring 500 includes three indentations 510 foraligning it with jar 450. Ring 500 may further include a plurality ofopenings 520 to allow drainage of the preserving solution from jar 450after removal of the top cap. Any number of openings 520 may be formedin ring 500 and the shape and size of the openings may be varied asdesired. Ring 500 may further include a plurality of channels 530adapted to receive the retaining elements 118 described above. Thenumber of channels 530 may be the same as the number of retainingelements 118 on stent 102. Channels 530 may be evenly spaced about theperimeter of ring 500 when retaining elements 118 are evenly spacedaround the perimeter of stent 400. As illustrated, ring 500 includesthree channels 530, although it will be understood that the ring mayinclude two, three, four, five, six or more channels.

The cross-sectional shape of channels 530 may be varied, and may bedependent upon the shape of the retaining elements 118 to be receivedtherein. FIGS. 6A-6D illustrate a series of retaining element-channelinterfaces. FIG. 6A illustrates a retaining element 118 similar to thatshown in FIG. 2 within a channel 530 of ring 500. Channel 530 mayinclude a beveled top surface 535 to properly locate and seat retainingelement 118 in the channel. The same or similar retaining element 118may also mate with a channel 530 having a square recess 540 in its topsurface, as seen in FIG. 6B. In other examples illustrated in FIGS. 6Cand 6D, channels 530 may have a beveled top surface for accepting squareor diamond-shaped retaining elements 118. It will be appreciated thatthe bevel angle illustrated in FIG. 6D is steeper than that of FIG. 6C.Thus, the angle of the bevel of channel 530 may be selected toaccommodate various retaining elements 118.

In operation, a fully assembled prosthetic heart valve 100 may be placedin a jar 450 having glutaraldehyde or other preserving solution. Ring500 may be correctly positioned over jar 450 by aligning the clips 460of the jar with the indentations 510 of the ring. Certain struts 114 ofheart valve 400 that include retaining elements 118 may be guided intochannels 530 of ring 500 and allowed to naturally radially expand untilthe retaining elements are affixed within the channels. Once allretaining elements 118 are mated within ring 500, a top cap, such as ascrew cap, may be affixed to jar 450 to seal heart valve 400 within thejar. Jar 450 may then be transported to a hospital or clinic for use.

Once at the use location, the prosthetic heart valve 400 may be removedfrom jar 450 as will be described below. Ideally, prosthetic heart valve400 is removed from jar 450 using aseptic techniques to maintainsterility and avoid contamination of the valve.

A tool 700 may be used to detach ring 500 from jar 450. FIG. 7Aillustrates the use of tweezers to pull ring 500 off jar 450. It will beunderstood that a hemostat, forceps, clamp or other similar instrumentmay likewise be used to remove ring 500 from jar 450 or that manualremoval of ring 500 using fingers may be possible. As seen in FIG. 7A,tool 700 grasps a portion of ring 500 and pulls it to decouple it fromjar 450, disengaging clips 460 from indentations 510.

FIG. 7B shows a similar concept, but includes a tool having a threadedshaft 710 that mates with a threaded aperture 550 in the center of ring500. Instead of being threaded, shaft 710 may instead be press-fit orsnap fit into a non-threaded aperture in the center of ring 500 toremove the ring from the jar as seen in FIG. 7C.

Regardless of the method of detachment, once ring 500 is decoupled fromjar 450, prosthetic heart valve 400 remains attached to ring 500 via theretaining elements 118.

FIG. 7D illustrates a stent 400 coupled to a ring 500 being removed fromjar 450. For the sake of clarity, stent 400 does not include a valveassembly, although it will be understood that a completely assembledprosthetic heart valve 400 includes a valve assembly.

Prosthetic heart valve 400 may be rinsed in a solution 730 while stillbeing secured to ring 500, as shown in FIG. 7E. The rinsing solutionmay, for example, include a 0.9% sterile saline solution. Heart valve400 may be immersed in rinsing solution 730 simply by grasping ring 500,without the need to contact the valve, thereby reducing the likelihoodof contamination and damage to the prosthetic heart valve.

Using tool 700, ring 500 may be maneuvered to place prosthetic heartvalve 400 in a support member 750 of a valve loading system, as seen inFIG. 7F. At this juncture, retaining elements 118 of heart valve 400 maybe decoupled from channels 530 of ring 500 by sliding each retainingelement 118 radially inward until it clears its associated channel 530.The retaining elements 118 may be decoupled from the channels 530together or one at a time. FIG. 7G illustrates heart valve 400 afterbeing loaded into support member 750 and removal of ring 500. Prostheticheart valve 400 may now be ready for loading into a delivery deviceusing the valve loading system. Thus, heart valve 400 may be shipped,transferred and loaded with minimal handing.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

It will be appreciated that the various dependent claims and thefeatures set forth therein can be combined in different ways thanpresented in the initial claims. It will also be appreciated that thefeatures described in connection with individual embodiments may beshared with others of the described embodiments.

The invention claimed is:
 1. A kit for holding an implantable medicaldevice, the kit comprising: an implantable medical device including acollapsible and expandable prosthetic heart valve having i) acompressible stent including a plurality of struts and having an inflowend and an outflow end, selected portions of the stent forming retainingfeatures on the outflow end of the stent for mating with portions of adelivery device, and ii) a valve assembly; a jar for receiving theimplantable medical device, the jar having an open end and a closed end;and a ring coupleable to the open end of the jar, the ring having aplurality of channels adapted to receive the retaining features of theimplantable medical device to stabilize the medical device within thejar.
 2. The kit of claim 1, wherein the ring further comprises aplurality of openings through which a liquid may be transferred.
 3. Thekit of claim 1, wherein the jar includes a plurality of clips and thering includes a plurality of indentations capable of mating with theclips to lock the ring to the jar.
 4. The kit of claim 3, wherein theplurality of clips are evenly spaced about a circumference of the jar.5. The kit of claim 1, wherein the plurality of channels extend radiallyin the ring.
 6. The kit of claim 1, wherein the plurality of channelsinclude three channels.
 7. The kit of claim 1, wherein the plurality ofchannels are adapted to receive a circular retaining feature of theimplantable medical device.
 8. The kit of claim 1, wherein the pluralityof channels are adapted to receive a diamond-shaped retaining feature ofthe implantable medical device.
 9. The kit of claim 1, wherein theplurality of channels are adapted to receive a square-shaped retainingfeature of the implantable medical device.
 10. A system for transportingan implantable medical device, the system comprising: an implantablemedical device including a collapsible and expandable prosthetic heartvalve having i) a compressible stent having an inflow end and an outflowend, and including a plurality of struts, selected portions of the stentforming retaining features at the outflow end of the stent for matingwith portions of a delivery device, and ii) a valve assembly; a ringcoupleable to the implantable medical device and having a plurality ofchannels adapted to receive the retaining features of the implantablemedical device.
 11. The system of claim 10, wherein the ring furtherincludes a plurality of openings through which a liquid may betransferred.
 12. The system of claim 10, wherein the plurality ofchannels extend radially in the ring.
 13. The system of claim 10,wherein the plurality of channels include three channels.
 14. The systemof claim 10, wherein the retaining features are sized for introductioninside the delivery device.
 15. The system of claim 10, wherein the ringincludes a continuous outer circumference that is uninterrupted by theplurality of channels.
 16. The system of claim 12, wherein the ringdefines a plurality of inner voids, each of the plurality of inner voidsbeing in communication with one of the channels adjacent a center of thering.
 17. A system for transporting an implantable medical device, thesystem comprising: an implantable medical device including a collapsibleand expandable prosthetic heart valve having i) a compressible stentincluding a plurality of struts, selected portions of the stent formingretaining features for mating with portions of a delivery device, andii) a valve assembly; a ring coupleable to the implantable medicaldevice and having a plurality of inner voids and a plurality ofchannels, each of the plurality of channels extending radially from oneof the plurality of voids toward an outer circumference of the ring andterminating before the outer circumference of the ring, and beingadapted to receive the retaining features of the implantable medicaldevice, each of the plurality of inner voids being in communication withone of the channels adjacent a center of the ring.